Optical and optoelectronic devices find many applications in e.g. telecommunication networks and metrology. The devices in the aforementioned fields may comprise active devices such as lasers, amplifiers and detectors, and passive devices such as filters, polarizers and absorbers. In general, key parameters of these devices are power consumption (for active devices), stability which dictates the lifetime of the device and various parameters related to the function of the device; the functional parameters may include e.g. saturable absorption of electromagnetic radiation, polarization dependent absorption of electromagnetic radiation, internal and/or external quantum efficiencies etc.
Novel nanomaterials including e.g. nanotubes, nanowires, fullerenes, quantum dots, nanoparticles and nanowhiskers present a new way to tailor the key parameters in optical and optoelectronic devices. E.g. nonlinear optical effects may be introduced to and enhanced in a device by using these nanomaterials at a suitable location in the device structure. Although the new nanomaterials and nanostructures show promise in improving key parameters of optical and optoelectronic devices, the materials simultaneously present new challenges to the fabrication of these devices.
The method for the synthesis of nanostructures is strongly dependent on the structure itself. Some nanostructures e.g. quantum dots may be synthesized in a conventional thin-film deposition tool such as an MOCVD tool whereas fibrous network structures comprising e.g. nanowires may require a tool specifically designed for the synthesis and/or deposition of these high aspect ratio molecules (HARMs). The fabrication of devices comprising the new nanomaterials often requires manipulation of material at a molecular resolution. This is especially important in optical devices comprising HARMs where the specific orientation of a molecule with a high aspect ratio may significantly affect the optical properties of the device. An example of such a device is a polarizer (or polarizing filter) whose optical transmission coefficient depends on the polarization of incident light.
Additionally, of paramount importance in optical applications is the purity and homogeneity of the nanomaterial. In order to incorporate HARMs in a device the molecules are filtered from e.g. a gas stream and/or dispersed in a solution. These operations risk the incorporation of impurities in the optical device and the dispersion of HARMs in a solution is commonly insufficient to result in homogeneous material. Moreover, dispersion often requires the use of harsh treatments such as sonification and/or the use of surfactants and functionalizing materials, which may be detrimental to the operation of the device.
The performance of many of the currently known optical and optoelectronic devices based on nanostructures suffers from the difficulties in fabrication as well as from properties of the functional nanomaterial. For example publication WO2008/025966 A1 discloses a composition comprising nanomaterial in an optical coupling gel or an optical adhesive. The invention disclosed in publication WO2008/025966 A1 suffers from inhomogeneous dispersion of the nanomaterial e.g. nanodots in the optical gel or adhesive. It may furthermore be difficult to obtain nanomaterial of sufficient purity for optical or optoelectronic devices from the nanomaterials disclosed in the publication.
For the improvement of existing, and for the development of new optical and optoelectronic devices it is important to find new nanomaterials with improved functionality, purity, versatility and homogeneity. Equally important is to develop new manufacturing methods that do not result in degradation and do not detrimentally alter the key properties of the materials utilized in these devices.